Configuring Fman interfaces for Jumbo frames

[vboroda]

I made a Yocto Dunfell build for a custom T2080-based board with QorIQ kernel 5.4.3. 

All interfaces generally work, SFP and Ethernet.  The config parameters are as follows:

CONFIG_FSL_DPAA=y
CONFIG_FSL_FMAN=y
CONFIG_FSL_DPAA_ETH=y
CONFIG_FSL_XGMAC_MDIO=y

However, the maxmtu for all FMAN interfaces is set to the Ethernet default of 1500.  Setting fsl_fm_max_frm=9600 in the kernel boot parameters doesn't appear to affect maxmtu. The kernel sources indicate that the FSL_DPAA_ETH_JUMBO_FRAME config parameter only applies to the "SDK" builds.

Can we get jumbo frames working on the non-SDK build?

[Oswalag]

It could be possible but we don't have any example out of the SDK.

In case you are interested, Linux SDK supports Jumbo frame size up to 9.6KB. The driver has the option to allocate Rx buffers large enough to accommodate the entire frame(of max 9.6K).

In addition to enabling this feature(FSL_DPAA_ETH_JUMBO_FRAME) from menuconfig, the user is required to set the L2 maximum frame size to 9600, otherwise the configuration is not valid. This can be achieved by either setting fsl_fm_max_frm=9600 in the bootargs, or configuring CONFIG_FSL_FM_MAX_FRAME_SIZE from menuconfig.

[temax]

Thanks, Oswalag! I actually went to menuconfig and the option FSL_DPAA_ETH_JUMBO_FRAME is not there for my Layerspace LS1046A RDB. Also, it is not in my target/linux/layerscape/armv8_64b/config-5.10.

I also tried adding fsl_fm_max_frm=9600 to my bootargs and double-checked the kernel received it properly by looking at /proc/cmdline, but it still did not do anything. It did not either read it or apply it.

It seems it is not psosible or easy, at least, to change the max frame size, even if you change it in the fman.c

Any idea on how to change it?

Thanks a lot!